Heterogeneous nucleation of gallium with lattice-matched cubic carbide and nitride phases

Abstract

Energetic barriers to nucleation can result in metastable liquids, which require additional undercooling to initiate solidification. Gallium, a low melting point metal of potential use as a phase change material and for liquid metal electronics, exhibits a well-documented temperature-dependent undercooling that can exceed 60 °C in small volumes (10 μl) cooled at moderate cooling rates (10 °C/min). Here, we use an epitaxial lattice-matching technique to identify cubic carbide and nitride phases that could serve as nucleation catalysts for gallium and gallium-based eutectics. We demonstrate multiple cubic carbides and nitrides that reduce undercooling and show that the relationship between the lattice mismatch and observed undercooling conforms with the heterogeneous nucleation theory. HfC and ZrN result in the smallest reported undercooling to date, <20 and <10 °C, respectively, across all equilibration temperatures after aging. These materials remain stable, even after aging for 120 days in liquid Ga. The carbide and nitride phases described here are commonly used as hard coatings and diffusion barriers, suggesting their practical applicability as thin coatings that both protect an underlying device or component and simultaneously reduce undercooling of gallium or gallium-based eutectics.